We wish to continue our studies on peptide metabolism by lung enzymes. Although peptides have many different actions, they can have common metabolic pathways by being cleaved by the same enzyme. This could determine their duration of action and potency. Besides angiotensin I converting enzyme (kininase II; ACE), the importance of other enzymes that are present in lung tissues and in blood cells, which can accumulate in the lung, will be investigated. Special emphasis will be on the neutral endopeptidase 24.11 (enkephalinase or NEP) that we detected in human lung and neutrophils. The ultrastructural distribution of NEP will be compared to that of ACE in human lung by using the immunogold technique we previously employed with other organs. In situ hybridization will locate the sites of synthesis of NEP in the various cell types. The distribution in and mode release of NEP from cultured human fibroblasts and isolated human neutrophils will also be studied. Because NEP is a putative inactivator of several peptide substrates outside the central nervous system, we will characterize its activity on VIP and other peptides acting on the lung and the actions of ACE on the VIP fragments. The involvement of serine proteases of leukocytes in the metabolism of active peptides will be also studied by several techniques, including bioassays, RIA and HPLC. Specific inhibitors of peptidases will also be used to characterize the enzymes involved.